text:
Why did the FAA ban all supersonic flights over the United States, rather than only supersonic flight in densely-populated areas?
A major part of why the Concorde was far less of a hit than predicted, and of why the many 1980s and 1990s supersonic transport projects never got off the drawing board, was that the FAA had banned all commercial supersonic flights over the United States in 1973 (two years after the original U.S. SST effort collapsed) due to concern over sonic booms, locking SSTs out of the lucrative U.S. transcontinental routes.
Given that transcontinental supersonic flights could have been flown with minimal disruption on the ground by routing them mainly over sparsely-populated areas and using brief periods of subsonic flight over major population centers (here is a map of some possible routes), why did the FAA impose a blanket ban on commercial supersonic flights, rather than merely banning supersonic flights over or near densely-populated areas?

The opinion I heard on this was „to prevent a European aircraft from capturing 100% market share with US airlines“...

Because those of us who live in sparsely-populated areas don't like sonic booms, either!  Indeed, you could turn your question around, and ask why not allow supersonic flight over heavily-populated areas, where it's so noisy that the urbanites would scarcely notice the extra boom or two.

When you want to know why the FAA or any other US government agency created a rule, the answer will be found in the Notice of Proposed Rule Making (NPRM) that is required to published prior to implementation of a new rule (with limited exceptions for emergency rules). All NPRM are published in the Federal Register, after which there is a period for public comment. After that, if it is implemented, there will be another notice in the Federal Register that summarizes the proposed rule, addresses the public comment and provides the final rule and the date of effectiveness.
In this case, we can go to the Federal Register for April 16, 1970 and on page 6189, we have the NPRM. As the online document is an image scan and the full NPRM is about 2 pages long, I've included the following relevant image clips:

The last paragraph specifically answers the posted question stating:

Because of the changing patterns of population within the United
  States, it is not believed that a general regulatory definition of
  "populated" land areas can be established that would provide the
  necessary protection from sonic boom. For this reason, the proposed
  rule in effect prohibits the operation of any civil aircraft within
  the United States at a speed that would cause a sonic boom to reach
  any part of the surface of the United States, except the territorial
  waters.

You can review the full NPRM at the link above. The final amendment, Amdt. 91-112, was published in the Federal Register on March 28, 1973 page 8051, and includes responses to the public comments received.

The stated rationale doesn't stack up - if changing population patterns are the problem, then the proper response would be to change the permissible and forbidden areas every so often to account for the changes in population distribution, rather than to figuratively throw one's hands up in despair.

@Sean  You haven't worked much with government lawyers and bureaucrats, have you? First, where do you draw the line between populated and 'not' populated? It needs to stand up to legal scrutiny. If you can get past that, if the population shifts the rule isn't effective. Sure, you can redefine it, but that takes time (this rule took 3 years) and in that time the rule is deficient. So during that time it is in violation of the law (Section 611 of the FAA Act of 1958). Rules implement laws. They're can't be vague and flexible.

Direct answer – Some weather patterns can cause some booms to be heard tens of miles away and urban and suburban growth was quickly extending into formerly rural areas, so the theoretical corridors weren't going to be practical.
Background – I lived in both rural and urban areas during the years while supersonic flight was allowed. While the noise did not much bother me at my young age, sonic booms woke sleeping babies and night-workers (you really want a dead-asleep doctor trying to save your life?), scared toddlers, animals, and some people, broke windows (many tract homes in those days had thin walls and windows), interrupted all sorts of people in focused activity (try to focus swinging a bat at a ball while being hit on the head or working on finances), and startled about everyone.
Concorde – None of this affected the Concorde, as its purpose was to fly between Paris and New York City. The Concorde passed into engineering history because (1) the long term economics lacked enough people with desire and money to make the Concorde a viable business, and (2) sonic speeds vibrations and drag and heat-expansion are much more severe than at subsonic speeds, and complicated design and maintenance beyond a profitable price-point. Shame, as it’s a beautiful aircraft.

Because people living in rural areas don’t like having loud, noxious sonic booms damaging their property and aggravating them at all hours of the day while these flight tiptoe around urban airspace and don’t annoy city dwellers.  And they vote and have representation in Congress.


text:
Why don't tanker aircraft have ejection seats?
Apparently, the KC-135 has no ejection seats (they used to have parachutes to allow the crew to manually bail out, but those were removed in 2008 to save money), and, according to this Quora discussion, that's the case for all tankers (presumably excluding the ones converted from bombers), not just the KC-135.
This seems somewhat illogical to me, as tankers act as potent force multipliers; to quote the linked post:

It is quite possible that a sophisticated opponent will go after the tankers, as an easy way to disable a lot of aircraft without actually having to shoot them down. Doesn't really matter if they go down from a missile hit or lack of fuel. The math on that one looks very good - shoot down a tanker, and you have probably shot down four or five smaller, agile, hard to hit strike aircraft.

Not only that, but tankers are big, slow (for military aircraft), and generally devoid of any defensive armour or armament, making them easy targets relative to combat aircraft.
Even in peacetime, the role of a tanker aircraft inherently places it at a much greater risk of a midair collision than most aircraft are ever exposed to (example) - and, with most MACs, the only way to survive is to abandon aircraft.
So why don't tanker aircraft have ejection seats for their crew?

Tankers are big, slow, and devoid of defensive measures because they don't need any of that. They're used from a very safe distance, and if there is a risk of enemy air power, friendly air power runs interference. Great question though!

crew of KA-6D tankers, EA-6B and F/A-18 aircraft etc. etc. relegated to tanker roles had ejection seats. So your statement is not universally true.

When I was flying the KC-135 tankers - A model and Q models - all crew members had parachutes, and all parachute packs had supplemental oxygen bottles that were good for at least 10 minutes - which was enough time to descend to the point where you did not need supplemental oxygen. If you had to bail out, it would be through the crew entry hatch, on the port side just behind the pilot's seat and in front of the boom operator's seat. If you had to pull the handle for bailout, the crew entry hatch would be jettisoned and a metal air dam would be pneumatically deployed about 4 feet down at the leading edge of the hatchway, to provide a wind block to allow crew members to fall free of the aircraft before getting into the slipstream. This prevented crew members from being blown back onto the body of the aircraft.
I have never heard of any tanker crew ever having to bail out of a KC-135, so perhaps this is why they got rid of the parachutes? Of course, I retired more than 20 years ago, and much has changed since then. But the KC-135s are still flying, even though they are older than anyone flying them today.
To answer the original question - both the KC-135 and the KC-46 are modifications of civilian aircraft, which do not have ejection seats; whereas fighters and bombers are designed for their specific mission.
Finally, I'm not aware of any cargo aircraft that have ejection seats, either.

Welcome to aviation.SE!

Welcome and thanks for your service!

Primarily because tankers and transports are being operated in non-combat environments or safely benhind the front lines of a battlefield so ejection seats are not absolutely necessary for crew survival.  The redundant capabilities of large multi-engines aircraft are such that there are minimal risks of ending up in situation where escapes systems are necessary.
People have commented that taker or transport aircraft cannot incorporate ejection seats because of the design features of large aircraft.  This is false as large combat aircraft such as the B-2 and B-1 bombers are fitted with ejection seats at all crew stations with jettisonable or frangible hatches above the seats to facilitate ejection.

It is mentioned in other answers, but I want to point it out explicitely: it's the tanker's role, and to a lesser degree its origin.
Big tankers, such as the KC-135, let's call them fleet tankers, are a flying gas station well away from the front line serving all aircraft in the theater of operations, e.g. in- and outbound fighters, the AWACS if present, and all other you find useful in your operations.
Any large plane well away from danger simply doesn't need ejection seats, since you can always withdraw them if enemy fighters come their way.
The exception to this rule (fleet tankers don't have ejection seats) are converted bombers, such as the Victor. Since, their design is a frontline one, i.e. the primary role was that of a bomber aircraft, they were designed to accomodate the dangers of frontline operations. In their role as fleet tankers they simply retained their ejection seats, because first why not, and secondly why expend money for removing something that does not interfere with normal operations.
Small tankers, i.e. buddy refueling, is used near or behind the frontlines to support individual attack aircraft. Their role is to support frontline operations, which carries inherent dangers. That's why we see buddy refueling capabilities with attach aircraft, such as the F-18. I venture, you will never see a small tanker without ejection seats fulfilling the role of a buddy refueling figher aircraft.

So first - let's talk about what has ejection seats: Fighter Aircraft.
When are ejection seats used?
Fighter jets have a glass/polymer dome above them for visibility. The area directly above their head is all one piece, and can thus be "ejected", providing space for a clean exit. There's not a ton of room, which is why pilots are limited to a certain height range, else they risk getting parts cut off when they eject. Ejections in general are pretty dangerous, and if the pilot lives, they often have serious injuries, like broken ribs, brain trauma, and so forth.
Structural
Tankers do not have a glass/polymer dome above them - they just have more of the fuselage. In order to eject safely, there would be have to large hatches above the pilots, copilots, and all crew seats in order to eject safely. This would be a point of failure for the fuselage, and cause extra complications and considerations throughout the engineering process. Even if they were successful in making this, there's a solid chance you would eject and get cut in half by the tail of the aircraft, which can be moving up to 580mph.
Seating
This would also mean that all crew members have to be seated in their ejection seats - which typically they aren't. Think of a refueler as a mobile home - you have a kitchenette, additional seating, and bunks to sleep in. Refuelers spend the majority of their time flying in straight lines waiting to be called upon, so they definitely don't stay seated all the time. You can actually find home cooking videos on Youtube made by Airman that are bored and making pizza during aerial refueling missions!
You also have to remember that there's a boom operator, who is either seated or laying flat at the back of the aircraft - ejecting him up would involve going through the tail, and ejecting backwards gets you stuck in the jet exhaust.
But what if they had ejection seats anyway?
In the case that they did have ejections seats, and every airman runs back to his seat before ejecting, there are decent chances they would either get cut up by the tail, bounce across the fuselage, or get sucked into the engine. All of which are pretty deadly.
But what about parachutes?
I can speculate as to why they wouldn't want parachutes. Jumping from an aircraft in anything but stable flight is dangerous, and nearly impossible. Jumping from a stable aircraft is also dangerous, unless it is built specifically for that. You would jump out the and get hit by the wings, the tail, or worst case scenario, get sucked into the huge jet engines. The KC-135 (or other US refuelers) is not built to be jumped out of like the General Aviation aircraft used by Skydivers.
Costwise, parachutes cost more than they should in the military (like everything else, including their 10,000 USD coffee mugs that they keep breaking), but the cost isn't prohibitive. The larger factor is that they take up space, as you need a parachute for all potential crew, and the canopies can be fairly large even when packed. Space is at a premium in this aircraft, and to add parachute storage would require removing something else. Beyond that, high-altitude jumps from cruising altitude would require additional breathing equipment, which would take up a similar, if not larger, amount of space.
It's not needed
In the end, it's unlikely a refueler will be shot down. Refuelers are generally only flown in areas where we have control of the airspace, or reason to believe that we are well away from enemy fire. Passengers aren't included in commercial jets, and the same reasoning applies to refuelers.

You make some good points, but despite sharing a lot of these challenges, bombers often have ejection seats.

@fooot They add ejection seats because bombers go directly above enemy territory. Refuelers are made to sit behind the "aerial front line" and provide a midway stopping point from home base to the battlefield.

Right, I think the main point is the difference in operational risk, where your answer seems to focus on the functional challenges, which have been solved before.

@Matt: Nevertheless, the nature of a tanker's mission requires it to stay within safe fighter range of the target (it wouldn't do much good otherwise!), which also means (assuming that the enemy's fighters have similar endurance to one's own) that it's well within range of the enemy's fighters.  Especially since the enemy's fighters won't have to fly as far as the fighters served by the tanker, except in the unlikely event that the target is the single closest airfield to the tanker.

@fooot Note that I don't say the challenges are impossible to overcome. They're just extraordinarily expensive, and are not worth the cost.

@Sean A refueler will never be out on it's own. Like I said, they expect aerial supremacy, and have fighters run interference for them. If a fighter is closing on a refueler, full of tens of thousands of pounds of jet fuel, they're already gone.

@Matt: So, if air supremacy can't be attained, the fighters and bombers have to do without any tanker support?

@Sean Pretty much. For the United States, the assumption is that we will always be able to have air superiority in some area due to overwhelming firepower and technology (though area that may be further away from the battlefield, making the tanker less effective, though still more efficient than landing.) The tanker would never fly directly over the combat zone unless we had air superiority there, as it's quite simply a sitting duck - they have basic defenses though, as you can never guarantee air superiority.. ask about defenses in a new question and I'll happily answer!

Firstly, any bail out above 20,000 feet has a low chance of survival without supplemental oxygen and tankers usually fly above that height. Also, bailing out of a plane going 450 MPH is an extremely dangerous activity with a high risk of death.
The bigger issue is that providing complex, oxygen bearing systems for the full crew would be expensive. Tankers are not supposed to be flying in any area where they would be taking enemy fire, so an evacuation situation would essentially be a freak event. Most of the scenarios where a tanker would be attacked have a low survivability anyway.
The only really serious situation where a parachute would be useful would be a case of mechanical failure or fuel exhaustion where the aircraft can make a controlled descent. Even in this situation, evacuation is problematical for several reasons:
(1) putting on a parachute properly takes a long time, unless you are already wearing it, there are very few situations where the crew would have enough time to strap into a parachute
(2) if you wear parachutes, it impairs your functionality; you are essentially gimping your performance every day for a 1 in a million event
(3) jets flight at high speeds, even if the crew slows them down for evacuation, so any jump will be highly dangerous to begin with, especially since you will jumping out a side door and can hit the aircraft after you jump
Basically, the probability of a parachute being useful is so low that it is not worth the logistical problems of providing them.

Points 1 and 2 of your answer are not entirely accurate. Your typical parachutes for skydiving, yes, they take a minute to put on (Instructors seem to slip into them in about 10 seconds though, so training could help), but emergency parachutes take much less time to put on. They've actually been proven that you can put them on in the air, which for anyone else that has skydived, knows that is an incredible feat. They're similar to a hiking backpack, with straps across the chest. You can put that bag on like a schoolbag, and jump, in a few seconds.

@Matt I am talking about the average person, not expert skydivers. I have helped people put on emergency chutes many times and it is not a process that would go well in the middle of an accident in a plane that is out of control.

@Matt  can gree with you but that is if the plane is in level flight or manovering really gentle. Of course if it's spinning in a wildly way it will hinder impossible to the crew to run for an exit, defeating any scape procedure anyway.

sorry chaps but a lot of rubbish. In RAF every crew member or passenger has a seat those that have to move around aircraft generally have a chest parachute which clips on to the harness which is always worn.Victor tankers have a max complement of 6. 2 (pilots) have ejection seats but other four have to open the door and jump. Same goes for the Vulcan bomber. They would most certainly not get hit by the tail, bounced on the fuselage or sucked into the engines, although  the Vulcan intakes are very close to the door.

Welcome to Aviation.SE! You answer could be improved by providing sources that could provide people with more information.

Also, how up to date is this? The RAF hasn't flown Vulcans since 1984 or Victors since 1993.

I seriously doubt everyone who's a passenger on one of the RAF Tristar tanker/transporters wore/wears parachutes.

Ejection systems have saved many lives in non-combat related incidents. When it comes to ejection, These systems should not be restricted to combat craft.  Ejection systems can be devised to work in almost any craft provided that the extra bulk is not an overwhelming part of the useful load.
By not including ejectors in more aircraft, designers are denying air crews the best lifesaving equipment there is. While it’s true that most aircraft go their whole life without crashing, some of them do crash eventually, some suffer from poor designs, malfunctions or pilot error, and yet we expect crews to go down with the ship. The reasons can include, cost, weight capacity and other performance considerations, but these are poor reasons to exclude life-saving technology.
This sends a message that your life is worth less than the cost of the system/design and the cargo capacity that you displace.  Ejection is by far the best option. It's self-contained, requiring only that you strap in to the same seat you always use and put on helmet. It requires far less reaction time. It can save your life far past the point that maneuvers become useless.  Depending on velocity and attitude, you only need a few seconds and a few hundred feet, to deploy the system properly. Even near the ground, ejection can be a survivable alternative to what would otherwise be a deadly crash landing or aborted take off. Good ejection systems are very expensive and sophisticated - operating as gyro-guided autonomous small rocket crafts in their own right.
The best way to think about ejection is to think about a pilot and crew over the span of their entire career. They may only need to use an ejector one time, if at all, but the number of lives it could save warrants it’s inclusion. It obviously makes less sense for passenger aircraft, due to the impossibility of including so many and the moral/ethical restraints against abandoning passengers. Nevertheless, It makes perfect sense for cargo-liners. Ejection systems for entire passenger craft/modules is fraught with difficulty and is not so close to being readily available tech, or nearly as viable as cockpit seats. But even these difficulties might be overcome if not for cost, efficiency, and 'return on investment' considerations. Ultimately, I f we really wanted to make such a craft because we considered lives to be invaluable, we certainly could. That said, it would be much more costly, burn more fuel, be heavier, carry fewer people, and cost more per ticket.
Such ideas can seem extreme, wasteful, or even crazy until you put things into the perspective of a situation where it would be the only thing that can save your life. The truth is, very, very few of us experience those kinds of situations and live to talk about it. Maybe we should give those voices more weight in such discussions - pilots whose lives may have been saved because this expensive, heavy, "crazy" equipment was there. In the end, usually, the main reason we exclude such systems is simply because we don't consider them to be 'worth it', not because we can't do it.

I disagree, there are other good reasons. For the tanker, the boomer don't have ejection seat (I don't think we can even speak of a "seat"). On another "aircraft", the space shuttle didn't have ejection seats for the lower decks (the one for the upper deck were removed)

You should reread this answer that give good arguments contradicting your answer and develop those points. Moreover, I don't think firing a rocket (the ejection seat mechanism) next to a failing tanker is the best lifesaving equipment.

Welcome to [aviation.se]! I managed to get through some of your post, and I think you've got some really good thoughts here. Please [edit] it to make it more readable, though. It's simply a "wall of text" and it's hard to read. A bit of organization and some paragraphs (as well as addressing some of @ManuH's concerns) will make this a much better answer.

DV as unreadable wall of text.

Welcome to the group! In the future, keep a few things in mind when answering posts: 1) Try to stick to the facts with supporting evidence, and less on speculative opinion. 2) For long posts, make sure to break it up into paragraphs to make it easier to read. I saw that you tried to do that, but it requires a double space on here for some reason. 3) Make sure to keep the answer focused on the question that you are answering, with fewer tangents and moralistic observation. Thank you for your post. I look forward to hearing more from you in the near future.

I’m not sure this is an answer.  As it is now, it is at risk for deletion since it is long and contains numerous speculative opinions.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Are there any airports that require arriving/departing flights to fly under an obstruction?
Are there any airports with approaches and/or departures that require pilots to fly under an obstruction at some point (thus meaning that, for at least a short segment of the approach or departure, there is not only a minimum safe altitude, but also a maximum safe altitude)?
I can imagine a few situations where this might occur, such as for an airport at the bottom of a deep, steep-sided valley with powerlines or a bridge across the top of the valley, but I don't know if any airports like this actually exist.

No, they do not exist.

It would not surprise me if someone, somewhere had done it, maybe even for good reasons (for example, possibly during the barnstorming era, one of the world wars, or perhaps on an Air America / POW rescue mission or similar) but thinking about an airport doing it as standard procedure brings to my mind phrases like "outrageously dangerous", "criminally irresponsible", and "out of your mind".
So I'm going to go with no, there aren't.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What does the code FU1FU2FU5 mean in this metar?
In their METAR, CYPK reported ... 25SM FEW037 SCT050 OVC250 21/15 A3016 RMK FU1FU2FU5 DENSITY ALT 400FT.
Since it's quite smokey out, I would have expected a simple FU in the weather section after visibility.
I'm wondering what FU1FU2FU5 is about. According to the remark format at http://meteocentre.com/doc/metar.html it should be "layer type and opacity in oktas". Is this just the way to say "sky covered by smoke"?

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How are METARs published?
I use https://flightplanning.navcanada.ca to get METARs and TAFs for my local stations. While listening to CYPK tower at work I noticed something in the header of my VLC:

That's a METAR! But why doesn't it show up at NAV CANADA?

That got me wondering where those reports/forecasts actually come from. After the station observes weather, does it report it to a central service? Does the station itself predict the future conditions to create the TAF?

The METAR for CYVR does appear a Nav Canada: https://flightplanning.navcanada.ca/cgi-bin/Fore-obs/metar.cgi

You posted a picture of the METAR for CYVR, a nearby aerodrome, and not for CYPK.

@ymb1 I thought that was part of the question, so I answered that below.

METAR
The METAR always refers to a specific airport and is obtained right then and there. That is at the airport.
It is a report of current conditions, usually hourly.
In the US, the FAA polls all systems remotely and disseminates the reports in METAR format. No word on wether this is via phone, mobile or radio, if that is what you are asking.
In Germany, the DWD, the german weather service, provides the reports. It can be assumed, that the situation is similar and that the stations are polled.
Weather stations have wide-ranging capabilities and operators, so the reported parameters may be different.
METAR reports may be reviewed by an individual before being transmitted, but the vast majority are reported automatically.
METAR reports are used for aviation weather, by definition, as a "Meteorological Terminal Area Report".
TAF
The TAF is a forecast. It is updated only 4 times a day and is provided by a human forecaster on the ground. Most larger airports have a meteorologist.
FORMAT
Both METAR and TAF use similar format, but each contains elements distinct from the other.  For example, a TAF may contain a FM (from) or BECMG (becoming), but a METAR never will.
DATA SOURCES
You can use https://www.checkwx.com/ to check both.
Or http://tgftp.nws.noaa.gov/weather/current/ if you want the raw data.

It sounds like the OP is aware that observations are made on the spot ("after the station observes weather"); he wants to know what happens next with the data.

Though this reference is second-hand information, the author suggests that the National Weather Service explains why some reporting stations do not get collated or transmitted by agencies like the FAA or Nav Canada. Here's what he says:

Many local airports across the state, as well as the country, have
  been fortunate to generate the funding to purchase AWOS equipment to
  obtain current weather conditions for their location. While
  establishing these sites however, they are generally not fully
  informed of the requirements needed to make this data available over
  the worldwide network used by the FAA and NWS. The FAA controls the
  stream of data from small airports such as these and requires the
  individual sites to purchase additional equipment and pay a monthly
  fee to send the data in to their system.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Where can one access the electrical buses in an aircraft?
I am looking at how new systems are retrofitted in aircrafts (large business jets or airliners), and I was wondering where the mechanics can get access to electrical power.
More specifically, I know that there is an electrical cabinet close to the cockpit, but are there any accessible AC buses elsewhere in the aircraft (for example, so that you don't have to run wires all the way back if you install something near the empennage)?
Thanks for your help!

Which aircraft?

General question for large biz jets and airliners. But for a start, info on the Challenger 605 or Gulfstream G550 would be very helpful

You want the fuses accessible to the pilot, so you are going to have to run a wire for the equipment up to the fuse panel in the cockpit anyway. Usually this is where you pick up off the AC or DC buss and add the appropriate fuse, then run the wires to the equipment.

The Challenger 605 electrical systems description is available from SmartCockpit here.


text:
Can airlines recover costs if they dump fuel for a medical emergency?
As per the title, can airlines recover costs if they dump fuel due to a medical emergency on board shortly after takeoff?

Probably they don't.

Why do you believe that they would even try? Fuel dumping is pretty rare...

Isn't that the role of insurance? In case of emergency, I would expect an insurance to compensate for any extra costs.

@ManuH Compensate any extra costs? That is certainly not the business model of insurers.

@bogl it depends how much they charge, but in case of an emergency, there role is also to remove the financial consequences from the decision process (e.g. better get the aircraft down to take care of a medical emergency than continuing flying it because it is expected at arrival and if it not there company would loose money). I also expect contract between insurers and airliner's to be highly complicated and required entire teams to optimize them (both for the airline and the insurer)


text:
What does automatic pitch trim is available mean, when bank angle is below 33°?
I was reading about the bank angle protection mode in an A320. I have a few doubts about it.
I know that if the bank angle exceeds 33 degrees then automatic pitch trim is not available and hence of the side stick is released the aircraft would come back to a bank angle of 33 degrees and stabilise. But I don't understand what happens if the bank angle is BELOW 33 degrees. I read that the automatic pitch trim is available. What does that mean?

In the context of the A320 as you are describing, pitch trim does not mean trimming with the horizontal stabilizer. Instead, it means that up to 33 deg bank angle, no aft stick pressure is needed to maintain horizontal flight, or more precisely, the load factor (for example, at 33 deg bank, the load factor is approximately 1.15g).
Up to 33 deg bank, the Normal Mode automatically commands the necessary load factor with the longitudinal side stick neutral. Since Normal Mode also ensures a neutral spiral stability up to 33 deg bank outside of High Speed Protection, you can maintain a coordinated level turn with side stick completely neutral.
Beyond 33 deg, longitudinal stick neutral no longer commands the necessary load factor for horizontal flight. Therefore, you would need to have aft pressure. Furthermore, there is positive spiral stability, which means non-zero lateral pressure is also required to maintain the bank angle.
For more information, you could consult: source 1 and source 2.

No need to worry about pitch when maneuvering.  Just the thing to degrade pilot flying skills even more.

Ok, so if the pilot makes a 25 degree bank to the right and then suddenly releases the sidestick (to neutral), would the aircraft continue to fly at 25 degree bank or would it return back to 0 degree (level flight)?

@Johnson If the aircraft is not overspeeding, then it would maintain 25 degrees bank with stick neutral (i.e. spiral neutral). Note that most, non FBW aircraft, would do this inherently, because spiral mode has a super long time constant.

@JZYL Ok, so how would the pilot bring the aircraft back to level, should he pull the sidestick to the left till it's level?

@Johnson Yes, lateral stick nominally commands roll rate (just like in any aircraft).

@JohnK I'm a lot more curious what pilots think of a pure Nz command without speed stability, which A320 commands

@JZYL my only jet time was on the CRJ with old school steam powered controls but there is a community debate over the discouragement of hand flying by airlines,and this extends to the philosophical tendency of Airbus FBW to move the pilot farther and farther out of the loop by automating much of the basics, like attitude control during maneuvering. Boeing tends to be more pilot centric than Airbus.Now if you ask pilots directly, a lot of them welcome the convenience of the automation options that FBW gives, but atrophied flying skills is an inevitable price that the industry is grappling with.


text:
Where can I find a free/cheap small airplane wing?
I am looking for a small airplane wing (e.g. Cessna 172, but not necessarily) to run some experiments prior to seeking an STC for a modification I am working on. Do you know where I can find a free abandoned wing, or a very cheap one? It doesn't have to be airworthy or functional at all, as I will just use it for standalone tests on the ground.
Thanks!

I'm in the U.S., and in Massachusetts if that's of any help

Google 'used airplane parts' - Wentworth comes to mind.  Be very clear you want something that is NOT airworthy - it will bring the price down a lot.  If you can get to Airventure, check out the FlyMarket

Thanks Dan, I'll be sure to check that out. I recently joined EAA and was already considering going to Airventure, so that's one more reason to go!

Wings may be tough to come by as they generally last the life of the plane and can be re-skinned/fixed if need be so they are not scrapped all that frequently. You can try a used parts dealer like this one or this one but they generally deal in air worthy parts which will not be cheap. Here is a guy parting out a 152 in FL he "has wings", you may want to give him a call and check other part out barnstormers adds.
Your best bet may be to wonder on down to your local GA field and ask some questions at the FBO or maintenance facility if there is one. Its more than likely someone has a wing or wing section that is no longer air worthy from some accident or the like. You may even just see a junked wing sitting in a field behind a hangar...
STC's are specific to part or aircraft/engine so testing on a generic wing may not be a good basis (depending on what  you are doing) you may want to get the wing from the aircraft you intend to STC.

Thanks a lot this is incredibly helpful! I'm having a look into all of that now. For the STC part of your answer, I 100% agree with you - the wing experiments I am going to run are to check and improve functionality of my system, but not to prepare for approval as I will have to work on the specific aircraft I am designing it for to get certified. I am just trying to reduce the time for which the aircraft is going to be grounded as much as I can.

@Aerocurious To add on a little to the answer specifically for you, you might want to check out Nashua-Boire Airport in NH because I have seen a section of really old planes that have been sitting there for years.

Awesome, I'll give them a call tomorrow. Thanks!


text:
When do birds generate more lift? Take-Off or Landing?
Good day! I am a student of aeronautical engineering and recently started studying the more natural way of flying, birds flight. After reading some scholarly articles there is still a question on my mind. Which phase of flight do birds generate more lift? My opinion is: in take-off. Knowing that birds jump in to the air without any contribution of the wings (just using leg thrust), the wings must generate enough lift to cancel the bird weight and make it climb and accelerate upwards. In the landing phase birds need to reduce the speed, and of course produce some lift to guarantee no harm to birds legs but the question is: is lift higher in landing or take-off phase? Does it depends on other aerodynamic parameters?

For a bird to stay at some height, lift must equal weight. If it climbs, this is because lift exceeds weight, and if it loses altitude, it's because lift is lower than weight.

@mins: unfortunately not quite true. If a bird is accelerating upwards (ie, vertical speed upwards is increasing) then lift exceeds weight, and if it is decelerating downwards (ie, vertical speed downwards is increasing) then weight exceeds lift. Lift is a force that provides acceleration, not velocity.

I totally agree with you. But for example, when the bird is landing, the lift is higher and the bird is losing altitude which means it is decelerating at that instant. But what I am trying to find out is f the magnitude of the aerodynamical force is higher in landing or take-off.

When the bird takes off, it goes from 0 -> TakeoffSpeed, the lift generated is just that needed to exceed the birds weight. As the bird lands, it goes from FullFlyingSpeed -> 0. Wouldn't there be more generated lift (negative) as the FullFlyingSpeed is without a doubt greater than TakeoffSpeed. But this also brings into question the time period. Do you allow the bird to take off to the same "FullFlyingSpeed", therefore changing the equation to 0->FullFlyingSpeed?

@Prodnegel I understand your point. It's indeed true that birds go from zero to the takeoff speed but they also need to be continuously producing lift in order to keep climbing. I don't agree with your definition of landing, since there is a clear preparation (approach) where they extend their legs and the wing movements are pretty different comparing to when they are flying at the full flying speed. And yes the time period is important too. I think that my answer is somehow related with the variation of momentum during takeoff and landing.

When V is obtained the bird needs to keep creating lift, but in that case, Lift will have the same value as its weight.

@EmanuelCamacho, you need to better define your question then. What time period are you considering here? The bird's mass does not change, therefore momentum would be directly calculated from the birds velocity, which brings it back to my original question of which velocity do you allow the bird to fly to? If bird takes off from 0->X in 3 seconds, but bird lands from X->0 in 4 seconds, then it would seem that the bird creates more lift taking off. Yes?

Also, it may be worth looking into gravity's effect here. If gravity helps the bird on its landing, then technically the bird would "generate" less lift by itself right?

@Prodnegel I totally agree with you from the definition of momentum. And yes, the gravity effect helps the bird decreasing their height even if in the very final phase is needed some lift to guarantee a smooth landing. Thanks for referring the time factor.

@EmanuelCamacho, Thanks for asking! I am sure a seasoned aviator will come to our rescue soon :)

@Prodnegel Thanks for bringing up those concepts. It made the problem a bit more clear, since I will try to introduce some other aerodynamically factors.

@EmanuelCamacho: This image depicts forces acting on an aircraft during a climb. Lift is oriented rearward, creating induced drag and providing some vertical force. Thrust is balancing drag and provides the missing vertical component to balance weight. The excess of thrust moves the aircraft forward. For a bird there is no engine, no thrust. The bird needs to orient its lift forward, and lift alone must compensate weight and and total drag, and provide some forward speed. Hence thrust is larger than weight in climb at constant rate.

@mins There is thrust in birds. The difference is that in our planes, the wings represent the aerodynamics while the engine represents propulsion. In birds the wing has everything included, in other words, the wings movement generates lift and thrust, due to the inverted Von Kármán vortex street.

@mins I understand what you said, because the thrust production in birds and even the aerodynamics of them are totally different from these days airplanes.

VTR - we already have a question about bird aerodynamics and it was decided that it would be on topic: Are birds aerodynamically stable?

@Peter mins is correct in stating that for climb, lift must be greater than weight. There is an initial acceleration upwards, which leads to a vertical velocity, which leads to an aerodynamic damping force downwards, proportional to climb speed. So in climb, lift = weight + damping force, which is greater than weight.

The easy answer is that they create more lift during take-off because the bird is heavier. Like aircraft, birds shed some mass during flight when their metabolism converts food to energy. Unless the bird picks up some prey during the flight, it will weigh less during the following landing and will also create less lift. But from now on I will interpret your question as if you had asked for the higher lift coefficient.
You cannot calculate bird flight with stationary aerodynamics (which is usually good enough for airplane aerodynamics). The flapping motion of the wings adds instationary effects wich dominate flow in case of birds.
Therefore, there is not one lift coefficient of a bird's wing, but a variation over flapping angle and angle of attack change, the integral of which keeps the bird in the air. If you want to get an idea how much lift can vary with the rate at which the angle of attack changes, please read this NACA report from 1951 (NACA TN 2525). Another hint: Birds with large wingspan, which prevents effective flapping while close to the ground, must run to reach sufficient flight speed, just like airplanes do. Watch albatrosses take off: They have to restrict flapping so instationary effects can contribute less to increase overall lift. Pidgeons, on the other hand, which flap their wings during take-off so much that their wingtips meet below their belly (and create the typical clapping sound of a pigeon taking off), can fly instantaneously when hopping into the air.
Now to your question: I have no hard data, only observations. They lead me to think that overall the lift coefficient during landing is greater. The bird uses full tail feathers down deflection to add more lift and moves the wings forward to compensate the pitching moment. This makes the whole configuration completely instable, but birds fly with "artificial" stability anyway. Only in this case they max out the lifting potential of all surfaces, fully knowing that inertia will not allow their bodies to become uncontrollable before their feet are on the ground or perch.

The only way the bird's mass is reduced during flight is if it "sheds" some poo. Although this is a quite likely event particularly for flights over humans this is not always the case.

First of all, thanks for your answer. Second, I was not even considering the mass loss during flight, and to be honest I didn't even think on that at all. Your conclusion, based on observations was that the lift coefficient is greater during landing, because of all the surfaces movement, but I have a question. For example, during a takeoff (escape takeoff is an interesting case too) does not the frequency of flapping increase the lift? The lift that you referred during landing can not be the drag, that helps the bird reduce its horizontal speed during approach?

@mezzanaccio: Nonono! It inhales oxygen and exhales the same oxygen as carbon dioxide and water. Guess where that carbon and hydrogen come from! Same happens with your body between meals.

@EmanuelCamacho: Right, the flapping intensity should contribute more lift and I did not consider that aspect. Maybe take-off does create a higher lift coefficient after all. However, it could also be that the flapping intensity goes into forward acceleration, and less into lift production.

@PeterKämpf Isn't acceleration in this case also lift (in the sense that a propeller generates lift, or perhaps a helicopter rotor)?

@Steve: No, during take-off the acceleration is mostly horizontal. Lift should be mostly vertical.


text:
Are there specific mass breakdowns for aircraft?
I am interested in the engineering and weights for aircraft around 8,059 lb (3,655 kg) Citation 505) and  18,900 lb (8,570 kg F-16).
Curious about specifically structural mass and landing gear systems. How much can landing gears lift?

Many information about mass page 223 of Aircraft design (Ajoy Kumar Kundu)

related: http://aviation.stackexchange.com/questions/7889/how-much-force-does-a-747-land-with

I can point you at some reference materials you can use. These methods involve estimates for different types of aircraft and formulas you can use to estimate the component weight based on the MTOW and OEW, for example.
You can use the following books:

Roskam - Airplane design (a series of books)
Egbert Torenbeek - Synthesis of Subsonic Airplane Design
Jane's All the World's Aircraft (over 600 aircraft)

scholar.google.com is another good source for finding articles about landing gear systems and design in general.

Could you include some details from those sources? As it stands this would be better as a comment as it doesn't provide an answer.

Welcome to Aviation.SE! As it stands, this is essentially a link-only answer, and those are frowned upon round these parts. How to write a good answer will help, as will taking the Tour.

@FreeMan: Guys, give Brilsmufffje a break. The question would need a very long answer, since you cannot just throw in a mass number. You need to define what exactly is part of the specific component and on what the number of equation is based. Weight data is traded between specialists like secrets are traded between intelligence agencies, and often the numbers you receive are unusable without a lot of background information. The sources he gives do provide this information and are what I would recommend, too.

Aeroplane landing gear is dimensioned for maximum weights, the weight data in OP is for empty weights. MTOW of a Citation II is specified as 15,100 lbs in Wikipedia, the F16-C as 42,300 lbs. From Torenbeek, Synthesis of Subsonic Airplane Design, category Light Aircraft.

There are two business jets listed with similar MTOW to the Citation II: the 1121 Jet Commander (now the IAI Westwind) and the North American Sabreliner. Empty weight of the Sabreliner is close to that of the Citation II and it is also a low wing mount, so I would expect the landing gear weight to be very similar = about 700 pounds.
For the F16: it is a fighter aircraft, with different design criteria than passenger aircraft. I cannot find freely available weight data for the F16, so a guesstimate would be based on the list of passenger aeroplane weight data in this answer for the VFW 614: about 1,600 lbs.


text:
How does an aircraft move on the ground?
Does an aircraft such as Airbus or Boeing have motors similar to cars, so that they turn the wheels?
or do they move on the ground with their engines, the same way they fly?

Or this one or possibly this one

For movement on the ground the aircraft uses it own engines, however since the aircraft cannot move backwards on its own, there are pushback trucks on the airport

A pushback truck lifts the front weel of the aircraft, their role in most airports is to move the aircraft away from the parking spot on to the taxiways. Here the truck is removed and when all platform staff is out of the way the engines are started one by one. From here on the aircraft moves on its own power to the runway. In the aircraft you will hear the engine spinning up when power is demanded for acceleration.

Not all push back trucks lift the front wheel off the ground. As a matter of fact, I've never seen one in the US. Usually they use a push bar that attaches to the nose wheel. Same net result, though.

And the engines are started well before pushback

@TomMcW  I've only rarely seen engines started before pushback.  On every flight I can recall, the engines are started during pushback.

A limited number of aircraft can move backwards using their own power.  Some turboprops and most members of the MD-80 family can execute a "powerback".  Ot happened very frequently at DFW.


text:
Can passenger weight shift cause a pitch shift in a commercial airliner?
If all of the passengers of an airliner, such as an A320, all moved to the front of the plane, like this, would it have the potential to cause the same result, (i.e. a change in aircraft pitch, potentially causing an incident at low altitude)?

I do know that I've been on a regional jet (like a CRJ, if I remember correctly), with about 15 people and they didn't want us to move around (switch seats) until after takeoff. I've also been reseated on a fairly empty flight with the reason being "weight and balance." I'd imagine that it could cause a shift in pitch if the airplane wasn't re-trimmed, but it probably varies by airline, and what their cargo load-out is as well.

@Canuk Interesting. An A320 weighs about 83,000kg, so I find it unlikely a 60 - 80kg shift in weight would do anything, but if that was 100 people... maybe an 800kg shift could do something...maybe.

Yeah, I kind of thought they just didn’t want us all switching seats. There were only about 15 pax if I recall...

There was a JetBlue flight some 10 years ago landing with their nose gear failed at hardover steering angle. I believe they asked passengers to sit as aft as possible before landing, so they could unload the nose.

For weight and balance calcs on an airliner the passenger seats are broken up into segments called zones, each one making up a number of seat rows.  There will be a minimum number of bodies required in each zone. It will be enforced at departure because centre of gravity issues are most acute during rotation and liftoff.  Once airborne it's not too a big deal unless a lot of people started to concentrate at one end of the other and the FAs would then intervene using their authority to force you to your assigned seat if necessary.

I was on an Air Canada flight out of SFO in the '90s on I think an A320, and after the door closed a flight attendant came to the very back of the plane, and asked a few of us to move far forward for weight balance at takeoff.  Would not have been more than four or six of us, all guys, I don't recall any really heavy specimens among us. She moved us all into business class seats at the front, obviously much comfier. As I buckled in I asked her if I could stay there for the flight, and she turned back to me, leaned in, in her best dog-training voice said "NO!", and went about her business.

@CCTO It was more likely an A340 I think. Funny story nevertheless xD


text:
Does the a320 neo have anything like MCAS?
I am trying to book a flight that will be on an A320 NEO.
Does this have any 'new' systems or features, like the MAX MCAS system?
I'm asking this question also because one airline has just grounded it's NEOs...

If you’re concerned about safety, I’d recommend to look for adequately trained crew and a positive safety culture in the company with much higher priority than for aircraft type. Admittedly, it’s very difficult to get these insights as a passenger.

Which airline 'has just grounded its NEOs'? I can only find reports of airline grounding specific aircraft due to issues with their Pratt & Whitney engines, and these reports go back over several months. Do you have a link?

@ReddHerring Exactly, and all of the NEOs use those engines. The engines are simply unsafe in their current state... https://www.indiatoday.in/fyi/story/mid-air-scares-what-are-a320neo-aircraft-and-what-s-wrong-with-them-1425443-2019-01-07

@cloud the article you link to actually says that there are two different engines for NEOs...

@cloud the problems with the P&W engines are well documented and have been known for some time. The article you link to makes that clear. Your assertion that 'one airline has just grounded its NEOs' is wrong, and not all the A32Xneo aircraft use P&W engines anyway. Once again you seem to be obsessing about safety issues that you barely understand and can't properly quantify in context.

I think the "grounded its neos" comment may be a misunderstanding of this news item about IndiGo grounding one of its A320neos for a hard landing inspection. Nothing to do with the safety of the type.

Different airplanes, different systems; however, all modern airliners have computer assisted flight controls to some degree.  These include stall protection of various types, of which Boeing's MCAS is one.  Airbus uses different methods of stall protection, but there's still a computer involved.
Do you need to worry about the same issue?  No.  Part of Boeing's problem was that they didn't tell people about their system and pilots weren't trained.  Had the pilots known about the system and how to disable it, the crashes probably would have been avoided.

There are many who argue (and at least one sort of successfully completed flight providing some evidence) that even with the then-current Boeing 737 MAX level of system knowledge, a total loss of control was not inevitable in the scenarios in question.

Downvoting for accident speculation. Your "had the pilots known" speculation even disagrees with the timeline presented by the preliminary report about the second (Ethiopian) crash. It seems that the pilots knew about the system and how to disable it, and they did, but were still not able to regain control of the aircraft.


text:
Was this 'load-balancing' seat change refusal real?
On Sunday, I was on a flight in Greece, on a A320. I was sat just forward of the wings. Someone sat in the isle seat opposite me, asked if she could move to the back to sit with her friend, since the seat next to her friend was free.
The cabin crew member said she'd check with the pilots, as the flight was almost full and carrying maximum fuel... strange. She then returned and said she couldn't move seats as it would affect the 'balance of the aircraft'.
I find it hard to believe a roughly 200lb human could affect a 183,000lb aircarft in any tangible way, but I wanted to ask if this would be a real reason for declining such a seat change?

@Sanchise, For me this is not a duplicate question because it has particularities: We should not neglect the possibility the Flight being almost full the pilot wanted the least encumbrance to the emergency exit door just behind since the person asking the question was sat just forward the wing. This explains the pilot refusal, but the cabin crew member gave the usual answer for refusal.

@DeltaLima, For me this is not a duplicate question because it has particularities: We should not neglect the possibility the Flight being almost full the pilot wanted the least encumbrance to the emergency exit door just behind since the person asking the question was sat just forward the wing. This explains the pilot refusal, but the cabin crew member gave the usual answer for refusal.

This is a VERY good video to watch about loading a plane.

@user40476 Your actual question, which you helpfully bolded and italicized for our convenience, is "if [aircraft balance] would be a real reason for declining such a seat change?" And the answer, as indicated in the linked question, is "Yes, it is". Now, that's not to say that one person moving would put the airplane out of its CG limit. ICAO (which Greece is part of) rules state that every airplane carrying people must have a properly calculated weight and balance report on board the airplane before takeoff, and the pilot may not have wanted to redo it just for one passenger.


text:
Is this safety ranking of different aviation methods accurate?
I'm compiling a list of essentially "Different ways a human can fly" and then ranking them in order of safest to most dangerous.
This is my final list, is it statistically (and practically) accurate?

Commercial flying internationally (airliners)
Commercial flying domestically
General Aviation (learning or as a passenger in a Cessna and the like)
Gliding
Paragliding / parachuting
Hang gliding

Sources/data - fatality ratios:

Commercial flying safety is well established and easily sourced
GA: 0.84:100,000 hours
Gliding: 0.7:100,000 flights
Paragliding: 2:10,000 annual pilot fatalities
Hang gliding: 1:1000 annual pilot fatalities

You are comparing apples and oranges. What is your definition of how safe? Per unit time or distance, per flight? In your examples you mix up fatalities per hour, per flight, per year! When doing something recreational (like gliding), you typically care about safety per time. But when flying commercially to a given destination you typically care about safety per distance, since that is fixed!

Adding to @Bianfable's comment, don't forget passenger distance. For some purposes, it's not unreasonable to statistically treat a C172 with four people onboard no different from a B747 or A380 each with four people onboard flying the same distance. (Whether such a substitution is reasonable from, say, an economics or operational point of view, is a completely different matter.)

I'm voting to close this question as off-topic because the answer is already included in the question and no specific concerns are raised about it.

If you're cruising around in a Cessna 172 with a decently maintained engine with lots of gas on a sunny afternoon, you really have to work at it to kill yourself.  It takes a random event of unbelievable bad luck, like the engine falling off, or severe incompetence.

Just because the answer to this question may be "no, this is not a good analysis" that doesn't make it a bad question. The question may be based on mistaken premises and other errors, but it can still be answered in a way that provides information and helps correct those errors. That makes it a good question in my opinion.

No, this is not a good way of understanding safety in aviation.
The figures you have may be accurate, but they are not figures describing the same things. You have figures describing fatalities per 100'000 hours, 100'000 flights, and per year.
In order to establish relative risk, you first must settle upon a common metric for each of these ways of flying, which is difficult, and if not arbitrary, is at least a choice you must make, excluding other useful choices.
The only reason a question like "Which form of flying is safest" looks simple is because it hide a great deal of complexity. You will need to ask a more sophisticated question, like: *Based on available data, in how many hours is it probable that an individual will experience a fatal incident, in each of these forms of flight?"

You seem to list the fatal accident numbers in the correct descending order, while leaving out a number for commercial flying.
"General Aviation (learning or as a passenger in a Cessna and the like)"
General aviation covers much more than your simplfied comment as noted in the FAA link you provided for a 2017 Nall Report covering data from 2015, while only addressing "The accident rate for GA non-commercial fixed-wing aircraft".
According to the Nall Report
"To put these numbers in context, we must look back even farther: In 1950, the
total accident rate was 46.68 per 100,000 flight hours; the fatal accident rate
was 5.17 per 100,000 hours flown. Fast forward to today: The accident and fatal
accident rates have plunged to an estimated 5.32 and 0.84 per 100,000 hours,
respectively. Clearly, we’ve come a long way in aviation safety"
https://www.aopa.org/-/media/files/aopa/home/training-and-safety/nall-report/27thnallreport2018.pdf?la=en&hash=C52F88B38FD95CB7C0A43F3B587A12E2692A8502
so I feel pretty safe flying my plane around.  Won't catch me jumping off a cliff or similar in a gliding suit, or out of a perfectly good airplane tho :)
General Aviation in the Nall report includes:
o Piston single-engine
• Piston multiengine
• Turboprop single-engine
• Turboprop multiengine
• Turbojet
• Helicopter
• Experimental
• Light Sport
It does not include:
o FAR Part 121 airline operations
• Military operations
• Fixed-wing aircraft weighing more than 12,500 pounds
• Weight-shift control aircraft
• Powered parachutes
• Gyroplanes
• Gliders
• Airships
• Balloons
• Unmanned aerial systems (UAS, or “drones”)

Why wouldn't you jump out of a plane? Skydiving is comparable safe to GA. Thanks for the answer though :)

I don't see any parachute stats in the list presented.  I'd rather fly down to the ground.  Only takes one mishap with a parachute to ruin your day, and I'd rather not go out that way.

For assessing GA safety (in all categories really, down to paramotors), you have to evaluate things from the standpoint of a non-idiot pilot, not just the raw statistical numbers, because the raw numbers are totally polluted by stupidity.
If you filtered out GA accidents caused by pilots doing stupid things; running out of gas, running into weather, crashing showing off, flying in conditions they shouldn't be, non bothering to check for water in fuel, and all sorts of other things, in other words, the accident rate for safe, prudent, sensible non-idiot pilots, I'm pretty confident you'll get a statistical prediction of getting killed that is down in transport aircraft territory.


text:
Can the NPPL exams now be taken online?
I can see that the CAA portal now offers PPL theory exams online from this article and by signing into the portal:

Can the 5 exams required for an NPPL(m) now be taken online?

They are taken on a computer, but at the ATO/DTO office


text:
Can I learn acrobatics in a Microlight?
Can I learn acrobatics in a Microlight, such as a C42 or Eurofox?
I would like to extend my abilities beyond getting from A - B but don't want to get a full PPL. I enjoy unusual attitudes too much :)

I would like to extend my abilities beyond getting from A - B but don't want to get a full PPL

You don't necessarily need a PPL to go do some aerobatics, go and visit someone like the British aerobatics academy at Fowlmere (fly your microlight in - great little airfield too!), and go with one of their fantastic instructors and have some fun.
Without a PPL, you cant add much by way of additional ratings. With a PPL, you can add a Instrument rating - both full and restricted (sometimes called an IMC rating in the UK). You could also add endorsements such as tailwheel, retractable, and variable pitch prop (colloquially: wobbly-prop). All of these things may well improve your skill, and enjoyment of flying beyond the "A-B and back again" that can get a little boring. But does come at a cost!
All that said, here's the answer to your main question.
C42
The C42 is not approved for aerobatics. It's type approval under "Permitted Manoeuvres" says:

Maximum bank angle 60º
Non Aerobatic
Normal acceleration limits, +4

Eurofox
Again, a good place to start is the type approval sheet and it too is not approved for aerobatics:

Maximum bank angle 60°
Non-Aerobatic
450kg/472.5kg - Normal acceleration limits, +4g /-2g
560kg - Normal acceleration limits, +4g /-1.5g

Hey Jamie, thanks for the answer... seems that they use a Genevation GenPro, which is under 650kg. So is it a microlight? I want to get to the point where I can do some of the manoeuvres in my own aircraft, so if there are no microlights approved for this, it wouldn't be possible

Early aerobatics and tuition will most likely use something like a Grob trainer. I would say its hugely unlikely you'd want to do any sort of aerobatics in a microlight. They're just not built for it.


text:
Could the Space Shuttle take off like an airplane?
This question got me thinking, would the Space Shuttle have been able to use its main engines to roll up to speed and take off horizontally like an airplane? (I'm not asking about getting to space, just flying around) What would the take off be like? What would forward flight powered by the main engines be like?
Did the space shuttle even carry fuel for the main engines internally? Before posting this question, I tried to find the answer myself, but I've had trouble finding any mention of it, only talk about the external tank. It seems to me you might want to have at least a little, just in case. If it did carry fuel, how long might it be able to fly for that way?
Would there have been anyway to put a usable fuel tank in the cargo bay?
(I realize that this will mostly be speculation, just asking for fun, if that's frowned upon, please let me know)

Buran did, but it didn't have the main engines, and required external ferrying jet engines for the trick.

Indeed, in terms of capability of the basic planform, the Buran atmospheric test article could take off with the added jet engines.  Also interesting to note if you look at the picture at https://en.wikipedia.org/wiki/OK-GLI that the nose gear strut is longer creating a positive angle of attack on the ground, not just compared to the shuttle's which is short, but compared to the spacecraft version of the Buran which seems to sit level on its gear.

Despite the scene in Moonraker the Shuttle orbiter carried no fuel for the main engines.
Further, the orbiter sat nose down on its landing gear, lacked the elevator authority to raise the nose off the ground at landing speed, and could not retract its landing gear (it used a straight-fall gravity deployment).  The OMS didn't have enough thrust or delta-V at sea level to accelerate the orbiter from a stop to flight speed, even without the pitch authority issue.

Thank you. I did wonder about elevator authority. Assuming there was fuel for them, I wonder if gimbaling the main engines would be enough to get the nose up.

They're set at a pretty high offset angle to counter the off center External Tank anyway -- I think the question might be whether you could avoid them just flipping the orbiter without that mass.  They were okay just before cutoff, but adding fuel mass in the cargo bay might "tip" things...

Can you cite a source for claiming that using OMS in the atmosphere was considered?

@BretCopeland Not offhand.  Shuttle Down came out well before the Challenger disaster -- the Shuttle may not have even been flying yet -- and additional planning on the part of NASA or pilots would have been done in the early 1980s.  I do recall reading G. Harry Stine (aka Lee Correy) writing that he'd spoken to shuttle pilots about the possibility.

Assuming that story is accurate, a science fiction writer having a conversation with some shuttle pilots about a hypothetical is a far stretch from "there were contingency plans". I'm very skeptical that NASA ever considered using the OMS in the atmosphere. The thrust to weight ratio is very low and there's very very little fuel left at the end of the mission. If they did consider it, I'd love to know about it, but without a source, it doesn't feel credible.

and the OMS certainly would never have been able to provide enough thrust to accellerate the shuttle to a speed where it could have positive lift. At most it might have been able to be used to provide some extra steerage during descent, kinda as an overpowered RCS system.

Aside from 007, Cowboy Bebop did the same thing

The cargo payload capacity of the Shuttle is about 22 tonnes when external tank weights 760 tonnes when full and is used up in 8.5 minutes. Hence it would be enough fuel for 14 seconds of flight. The thrust of the single engine, RS-25, 1860 kN, is more than three times that of the 777's GE90, 513 kN. Hence for 14 seconds we have near 5 times more thrust for about 2,5 times lighter machine (110 t vs 247 t). Hence I think it could take off and then glide while of course not into space. It would fly more like WW2 ME 163 Komet. It also may need adjustments of flight control surfaces as such flight is very different from that it usually does.

"5 times more thrust for about 2,5 times lighter machine" that would be an exciting take off!

Quick calculation suggests 5g of acceleration at start. Seems plenty.


text:
Would it be realistic to live in an airplane?
I've been playing with the idea of someday modifying a small airplane to create a sort of flying RV/Camper. The passenger seats would be removed and replaced with a flat, raised surface that would run along the wall to be used for a bed, or a desk during the day. A small chair and portable toilet could be secured below that, with room for food, etc.
Would this be usable in practice? Can a certified aircraft be modified in this way? Is it allowed to sleep in a plane on the apron overnight? Is external power ever available near airplane tie-downs? Etc.
I'm mostly asking about the U.S., but I'd be curious about other countries as well.

Too bad the name "Air Camper" is already taken.

You need to define “small”.  Most airplanes that you can actually stand up in don’t meet the common definition of small...

Oh, I wasn't thinking of anything big enough to stand up in. Maybe a Cessna 310 or something. Like people that live out of vans. Something you can get around in, sleep in, do some remote work in (why I care about a desk). Nothing crazy. My intention would be to spend most of my time at the location outside the plane.

I guess you're not talking about something like this, though it would be more roomy: https://www.buzznicked.com/planes-turned-into-homes/

Richard Bach had a short story (maybe in book "A Gift Of Wings") called "the 100,000$ sleeping bag") (don't remember actual number) about how uncomfortable seats in Cessna Skymaster were to sleep in, with the plane on the ramp at the airport...

Sure, it actually is more common than you might think. While the general notion of a private plane is a small sleek jet to dart about in, plenty of wealthily people own larger jets equipped as you describe. Nick Gleis is somewhat famous for photographing the biggest of the biggest private jets and this article covers a lot of the really cool stuff he has seen.
The FAA does not necessarily mind how you configure interiors as long as you don't try and qualify things as a "seat" for occupancy, takeoff and landing purposes.
Sleeping on the apron is likely more about airport rules than anything else. You would need some kind of an APU to run your electronics as most airports wont want you running your engines all night...
If it does not need to fly this is always an option.
While you likely cant order the cool defense stuff there is nothing stopping you from outfitting a VC-25 similar to Airforce One which is more than livable.

Most airports (at least in Europe) also won't let you run the APU all night (or anything longer than a few minutes after reaching your parking position / before pushback). So you'll need a ground power connection and possibly a PCA hose for air conditioning.

What do you need electronics for if you're just sleeping? It would be entirely possible to sleep in a non-running car with the battery disconnected; why can't you do the same in a plane?

Realistic yes, it's expensive and not that convenient. There are people who live out of RVs or boats, traveling around for years with no fixed abode and it works out fine because there's an infrastructure they can use. An RV can stop at a grocery store to stock up on supplies, get deliveries or food or shipping at campgrounds and RV parks. Boats can dock at large marinas, many of which have supermarkets attached. In both types of places you can hook up to electricity. Many permanent RVers pull a small car on a trailer, so they can range out from their campground, explore, resupply, take care of business, etc.
A large enough airplane could be converted into a flying RV, although I'm not sure how you'd set up cooking arrangements if it's a pressurized fuselage. There are some considerations and challenges to making it work:

Most airfields are far away from towns and cities which have amenities, or sites you'd want to visit. You'd need to be choosy about where you go
Airfields are not set up to provide convenient hookups to RV-style airplanes, you'd need a lot of batteries and limit yourself to low power applications. This is totally workable, just not as convenient as having a hookup. You could get a truck to give you power, which is expensive - you wouldn't want to have it 24 hours a day, presuming one was available
Transportation out of the airfield could be a problem in some places. Some FBOs have a courtesy car to borrow, some do not. Some areas have taxi services and some don't. You could probably pack a moped away somewhere to get around that, of course there's limits to how much you can carry on one of those
Airfields don't have convenient markets for re-supply, you'd need to leave the airport for everything
If the airport is commercial you may have to pass through security every time you want to get back to your airplane
If an airport has a closing time you may not be able to get to your airplane after hours
Some airfields will let you camp by your plane, some will not
Airplanes aren't designed for comfort when still, there aren't lots of windows you can open up to get fresh air. You'd likely need some sort of AC system, which requires power
You'll need to pay ramp fees, which are parking fees for your airplane. These vary a great deal from airport to airport, a small jet at a small rural field may be $10-$20 per night (cheaper than many RV parks!) and waived for a week if you buy fuel, the same plane at Teterboro, NJ would be $300 per night
It would cost serious money to re-do an airplane as an RV because the materials must be lightweight, and to get it certified will be expensive as it's a one-off build
Airplanes are very expensive to own and operate to begin with

None of these are deal breakers, it's just a matter of money.

I would disagree with most of these limitations. There are plenty of airports that are smack in the middle of cities, many have pump out trucks (for waste) and ground power. More than 50% of the fields I have flown to have courtesy cars and UBER is almost everywhere now. More airports than you think have food available. Ive never been to a field that I cant access my plane 24/7 (sometimes with some arrangement) even if its "closed", when in doubt the code is usually the CTAF frequency.... Windows can be removed...

Limitations was a bad choice of terms @Dave, there's nothing there that can't be worked around or lived with. They are more considerations, so I've re-worded accordingly.


text:
What airport is this?
A friend of mine asked for some help identifying the airport in the picture below. He needs it for a geocache.
Google reverse image search was, perhaps unsurprisingly, not very helpful. We've spent some time on Google maps, but there are many airports :-). Other than that, I'm really out of ideas.
We have some reason to believe that it is located in Europe, presumably excluding Turkey and Russia.

Could you provide the GC code for the geocache? That might give more clues.

@CatchAsCatchCan It's a German geocache and it doesn't have a GC code AFAIK, will check, though. Anyway, we've found it, will post an answer :-).

Besides the simple fact that his is an airport, what does the question have to do with aviation?

@MichaelHall I wasn't sure if it was going to be on topic, but the existence of the airport-identification tag settled it for me.

Brute forcing Google maps finally paid off. It's Bordeaux airport:

Wow, nice finding. I thought it might be in France because there are many roundabouts in the vicinity but that was merely a guess.


text:
What effect does wing loading (high and low) have on aircraft performance?
I've read that stalling speed is partly determined by wing loading. Correct me of I'm wrong - "Aircraft with high loading have more weight relative to their wing area hence the stall speed is increased (as the requirement for lift is increased)".
Also I've read that "faster aircraft have higher wing loading". I didn't quiet understand that statement.
And is wing loading weight/wing area, or mass/wing area?

Wing loading is, as a North American industry standard, defined as weight/wing reference area (W/S). But then again, there is nothing wrong to define it as mass/area; so be careful of comparisons against literature.
As you have correctly cited in your OP, a large wing loading inversely affects performance, this includes takeoff performance and turning performance, all due to increased stall speed. Assuming a constant maximum lift coefficient, the larger the wing loading, the higher the stall speed:
$$V_{{s}}=\sqrt{\frac{W}{S}\frac{2}{\rho C_{L_{max}}}}$$
Large wing loading, however, is beneficial from a ride comfort perspective and offers structural benefit (i.e. weight saving) when considering gust loads. Assuming the same level of gust, the faster an airplane flies, the higher vertical acceleration (G) it experiences. A particularly salient and approximate relationship can be found in 14 CFR 23.341 (pre Admt 64), whereby the load factor from gust is given by:
$$n_z=1+\frac{K_gU_{de}Va}{498(W/S)}$$
In the above, $K_g$ is the gust alleviation factor which increases with W/S, $U_{de}$ is the gust speed in ft/s (found in 23.333 and decreases with altitude), $V$ is equivalent airspeed in kt, $a$ is the lift curve slope. As you can see, the load factor decreases with increasing wing loading and increases with increasing airspeed.

For the purposes of weight and balance and expressing wing loading values, weight and mass are the same thing and the terms are used interchangeably (you will see "Weight and Balance" and "Mass and Balance" used in documentation).
So wing loading refers to the ratio of the area of the wings relative to the total mass or weight.  Wing loading is normally expressed, in North America, in lb/sqf, and in metric jurisdictions, in N or Kg/sqm.
As you go faster, the wing is able to support a given mass/weight with less and less total area, and it's more efficient overall, if your priority is to go fast, to reduce the wing area, while keeping weight/mass the same, to take advantage of that.  This is because the airfoil's most efficient AOA (max L/D) is at a fairly high angle and from a speed-efficiency perspective, you want to cruise as close to that AOA as possible to minimize induced drag.
The side effect of this is still higher minimum flying speeds than otherwise, but if your priority was to go fast, you live with that.  Wing flaps allow you to cheat your way, at least partly, out of this problem, by making your small wing work a lot harder at low speed than it would without flaps, then you can retract them so they are out of the picture when you want to go fast.
It's not that different really from water skiing on a small ski vs a big ski.  You can go faster on the "high ski loading" small ski, but it has to go faster to get on the step.
The small ski will also ride wavelets a lot better.  Same with wings; one benefit of small highly loaded wings is a better ride in bumps and you need that characteristic, since you are going faster, if you want to do it comfortably.
You see this effect clearly with light aircraft. The Thorp T-18 gets by on only 86 sqft of wing area at a gross of 1600 lbs, to cruise at 180 mph.  The Pazmany PL-2 has more or less the same overall configuration and all up weight, but has 116 sqf of wing area, a significantly lower wing loading, and cruises about 25-30 mph slower on the same power and most of that is due to the larger wings and lower wing loading.
The Thorp also lands and takes off about 10 mph faster, which is bad, but it also rides bumpy air way better, which is good (I own a PL-2 and have flown in a Thorp in the past).
The aviation gods giveth, and they taketh away...

"Weight and mass are the same thing. " No they aren't. In space, an object can be weightless, but it will always retain its mass. Weight is measured in N, mass is measured in kg.

Well you don't have to get all science-y.  For our purposes it is.  Airplanes for W&B purposes aren't measured in N, only kg or lbs, and the terms weight and mass are used interchangeably.

Newton is weeping in his grave.

Well you can write nasty letters to all the Weights Group managers at the various OEMs if you like.

Yes. "Weight" is just mass being attracted by gravity, so technically mass is the better term, but the world has been using the term "weight" forever.  But like I said, in North America at least, wing loading is expressed as pounds per square foot, based on all up weight, or mass if you will.

Your answer is the most correct of the bunch, but it could be more complete if you expanded why smaller wing is "more efficient overall". (Apart from structural reasons, it will always have less parasitic drag, and thus will have less drag overall at higher speeds). Also, another related "side effect" is reduced ceiling (given a limited max speed/Mach).

Added some stuff.

Wait, "14 deg or so" is around max L rather than "max L/D". The optimal AoA is much lower. Also, your explanation only holds if by "faster" you understand IAS. Otherwise one can say that with bigger wings, you can just fly higher, and that will also lead to a higher (~more optimal) AoA.

Optimal AOA for max L/D of the whole aircraft wing and body together yes because the wing is normally set at a few degrees incidence.  But the max L/D of the airfoil alone is up there at 12-15 deg but you'd have to set the incidence to that to have a level deck angle to exploit it, so it's totally impractical and is just used to illustrate the concept.  On speed, you have to relate it to IAS to keep things simple; otherwise you have to start accounting for altitudes and temperatures, adding needless complexity for the purpose of explaining a concept.

The AoA for max L/D of a typical airfoil is usually below 5°, which, "incidentally", is about the typical wing incidence angle. Max L (and so ~14°) is relevant for the discussion, but only in the context of takeoff/landing/stall. For optimum cruise, you want these 3-4°, yet with bigger wings and high speed, you'll have less, and that is the problem (in terms of L/D). As for speed, IAS is simple for us pilots, but not so for "normal" people. (I don't object though, it's just a note).

Yes my brain fart.  I took out some of the offending part.

On stall speed, as per this answer, the wing loading is defined as: $$\frac{L}{S} = C_L \cdot ½ \rho V^2$$.
L is the lift force provided by the wing, at 1g steady flight the wing only needs to counteract gravity, so L = W. Note that it is required to use lifting force L: in manoeuvres the wing needs to provide more lifting force, and the wing loading increases.
So with a given wing profile and $C_{Lmax}$, at higher wing loading the stall speed is higher.

faster aircraft have higher wing loading

Yes indeed, at constant $C_L$ and wing area S, more lift can be created at higher velocity. Or less wing area is required for a given lift compensating weight.

And is wing loading weight/wing area, or mass/wing area?

As stated, wing loading is lift/wing area, which becomes weight/wing area in 1g steady conditions.

The wing is always loaded by the lift force it generates. In 1G situations, the lift is indeed equal to the force that gravity exerts upon the mass of the aircraft - but it is important to realise in what circumstance this is valid.

That's the real wing loading.  But the comparison of weight to wing area gives an apples to apples, for example, if I compare my r/c model to a Cessna 152: my ratios of weight/mass to wing area are what?  That is why weight or mass can be used interchangeably.  Any units used for weight (or area) work to form ratios as long as terms are consistant.  Appreciate folks taking the time to discuss and work out these basics.

This is conflating wing loading $W/S$ and load factor $n$. $L/S$ = $n W/S$. Both expressions are mathematically correct but in terms of standard usage of the terms $L/S$ is not referred to as wing loading.


text:
What is transition altitude?
Now I know the definition of transition altitude - it's the altitude where pilots change their barometric altimeter datum from regional pressure setting to 1013.2hPa. In USA the TA is 18,000ft. But I just don't understand the whole concept. Why can't they just set the datum as 1013.2hPa at ground before takeoff. Why does it have to be 18,000ft. Also isn't the atmospheric pressure at 18,000ft much lower than 1013.2hPa, so isn't it wrong to put this as the datum?

Have a look at this answer including the "Further reading" section there.

This question covers a lot of the background to your question, and we have several others on the site about transition altitudes and levels.

The atmospheric pressure is dropping quite signigicantly with altitude - and this is the very point of the concept of the altimeter - messure the pressure and show this as an altitude.
The basic concept of a flight level is that all high flying planes share a common reference - and do not neet to consider local weather, which can change quite dramatically during a flight. The main topic here is traffic seperation - so all should use the same reference and thus can quite compare their altitudes.
But flying low there is a nice problem called "ground" - planes should mostly avoid it. On charts the minimum altitude is noted, as well as special places like airports. Here a more precise view on the altitude is needed - so pilots need to set their QNH. Before takeoff, before landing - or when flying low for a longer time quite frequently.
But where to change from one reference to another? That much depends on the location - in the US it is mostly 18000, but in other regions this can differ substantially.

But why do different countries have different TA's. Why can't all of them have a standard TA?

The datum setting is a sea level equivalent reference, it is not the actual pressure at the airport. The altimeter setting moves the whole scale up and down to provide an accurate altitude indication at the elevation for the reporting station. Usually this station is at an airport and if the runway is 3550 feet elevation the reported altimeter setting will result in an accurate altimeter reading when at 3550 feet. This is the only location and altitude where barometric altitude accuracy is certain to match true altitude. This is the best method to avoid contact with the ground and towers and good enough for separating local aircraft.
At altitudes above TA, all flights set the same standard setting for consistent aircraft to aircraft separation at high altitudes and over long distances. This is to reduce setting errors and because ground measurements are less accurate with increasing distance/altitude, and to reduce mistakes because of frequent adjustments in high speed aircraft.
Below TA speeds are generally much lower and flights are shorter so changing settings is less frequent and the flight is physically closer to the reporting station reducing atmospheric errors.
TA changes with country because they have different geography and different aircraft requirements, in the USA there are areas with 14000ft mountains, so it is not practical to have a TA below 18000ft. 18000ft is also the base of class A airspace in the USA and aircraft in class A are required to meet instrument flight rules, below is class E which can have VFR aircraft. VFR aircraft are allowed to use a standard altimeter, IFR requires a sensitive altimeter.
Historically aircraft did not have altimeters that could be adjusted in flight, they were all calibrated to 29.92 [1013.25] and then airport altitude adjustment was by hand calculation, with most low altitude flight segments accomplished visually. Many planes from that time did not have radio or had very poor radio, and prevented reliable reception of updated pressure settings. The calculations were both extra work for the pilot and not sufficiently accurate for high altitudes because of variation in lapse rates and temperatures and lack of weather reports. So everyone used non-adjusted indicated altitude at high altitudes.


text:
What does a reduction gearbox do in a turbofan engine?
I've read that the P&W PW1000G engine has a reduction gearbox. What is it and does it have any relation to the fan or compressor speed? Does it improve fuel efficiency?

The problem is that in bypass engines, the fan blades are much longer than the turbine blades that drive them. Both compressors and turbines should rotate as fast as possible, without shock waves occurring at the tip - so linear tip speed has an upper limit, meaning the compressor with longer blades must turn much slower than the turbine driving it.
This is what the geared turbofan does, reduces the rotational velocity relative to that of the turbine so that both can rotate at their optimum angular velocity. The forces involved and the required reliability make it not an easy design task, as noted in this answer,

Does it improve fuel efficiency?

It does, when both the fan and the compressor can rotate at their optimum speed, and when the gearbox does not add much friction.

The gearbox is located between the front fan and the rest of the engine. It lets the front fan spin at a lower rate than the main shaft.

Image source: aerospaceamerica.aiaa.org
The advantage of this setup is that the front fan can have longer blades to cover a larger cross-section area, while the low-pressure compressor and turbine blades in the core can spin faster to improve fuel efficiency.

Image source: www.aviationpros.com

You skipped a couple of steps between spinning faster and improving fuel efficiency. I mean, it is not so obvious, so it needs some explanation.

Certainly, one could write books about many topics. But at least some basic argument could surely fit in an answer here too.

@JanHudec Please feel free to contribute.

Sorry, but the part "while the low-pressure compressor and turbine blades in the core can spin faster to improve fuel efficiency" is incorrect. That is not where the fuel efficiency comes from. This answer is incorrect and I don't think others should improve the answer unless it is made a wiki answer (out of fairness).

@0scar, go for it!

@0scar, the need to maintain high rotational speed, while maybe oversimplified, is ostensibly correct. High efficiency and power density requires fast moving turbine and compressor blades, which is most easily achieved by them spinning fast.

The purpose of the reduction gearbox is to improve engine efficiency.
Normally in a turbofan engine the low speed turbine and fan are connected by a direct drive turbine shaft that requires the low turbine and fan to run at the same speed.  In a geared engine, the gearbox allows both the fan and turbine to run at their optimum speeds.  In this case, the turbine can run faster with fewer stages and airfoils, which increases efficiency.  The fan can run at a slower speed but at a larger diameter to push larger amounts of air at a slower velocity.
A simple formula for propulsive efficiency is:
$$ N = \frac{2}{1 + V_e / V_o} $$
Where $V_e$ is the exhaust velocity of the engine and $V_o$ is the velocity of the aircraft or inlet of the engine.
As $V_e$ lowers to the point where it equals the speed of the aircraft, efficiency N approaches 100%.  The larger slow moving fan in a geared engine allows large mass flow with low velocity which improves efficiency.  The low velocity also makes the fan quieter.

Got a source for the formula? Otherwise nice and concise answer. I edited in some paragraph breaks.

To increase the propulsive efficiency (total efficiency is the product of gas turbine thermodynamic and propulsive efficiency) we need to accelerate more mass flow less fast: this requires larger fan diameters. See e.g. this answer which describes how the bypass air provides thrust. The formula:
$$ F = \frac{\text{d}}{\text{d}t} p = m \frac{\text{d}}{\text{d}t} v = m \cdot a $$
shows that increasing the mass flow $m$ for the same amount of thrust requires less acceleration $a$.
This can potentially improve the fuel economy, but there is a limit, increasing frontal area will also cause the drag to increase.
As said in this answer, tip speed is a limiting factor, so we need to reduce the spool speed. The problem with decreasing the spool speed is that the work generated in the low pressure turbine (which is coupled by a shaft to the fan) needs a large diameter and more stages to get enough power from the gas to power the fan (let's not get too technical in discussing blade loading). A large low turbine diameter is not very effective for the bypass flow of the engine (how do you get the bypass air around it), therefore the spool speed of the low pressure turbine is increased to be able to use a smaller diameter. This mismatch in spool speed requires a gearing solution.
Note that very large amounts of power are being transmitted through the gear box, even with very high efficiencies this requires a lot of heat to be dissipated. Getting rid of the waste heat and the large loading has proven to be a very difficult design task.

The other formula you're missing is $KE=mv^2/2$ - which shows that the energy required to get something to a given speed increases exponentially; therefore a low acceleration will result in less energy being used

@UKMonkey: Quadratically, not exponentially.  In modern casual English I know "exponentially" gets used to mean anything that grows faster than linear, but we're doing physics here!  $e^v$ would be a very different formula, and dimensionally impossible.  (Exponents have to be dimensionless but $v$ is distance / time)

The preceding explanations are good.
But - interesting add-on is the notion that the gearing of a turbine is hardly a new concept - it's been around for decades in the form of turboprop engines.
The Allison T56 is an example of a geared Turboprop engine.   Simplistically, the difference between earlier turboprop designs and the more recent GTF design(s) - are the difference between a ducted fan and unducted propeller.

Yes indeed propellers have been geared down for a long time. The reason it had not been done for turbofans is the sheer size and forces involved. The fan is much larger than the prop, and requires proportionally much more torque to drive it due to the many more blades, each adding deg.